1. Field of the Invention
The present invention relates to a device for the wet-chemical treatment of substrates, particularly of solar cells, including at least one accommodation device, at least one substrate and at least one process medium being able to be inserted, or having been inserted into the at least one accommodation device; the at least one substrate having at least one treatment side which is able to be brought into, or is in operative connection with the process medium.
2. Description of the Related Art
For the production of solar cells, substrates are coated with various metal layers and semiconductor layers as well as buffer layers, by vapor-depositing, sputtering, by Galvanic deposition or by chemical bath deposition.
In particular, in the case of Cu(In,Ga)(S,Se)2-solar cells (CIGS solar cells), for the depositing of n-semiconductors, so-called buffer layers, a wet-chemical method is used, designated in English also by the term chemical bath deposition (CBD). In this context, the buffer layer includes cadmium sulfide (CdS), for example, undoped zinc oxide (ZnO), indium(III) sulfide (In2S3), and/or (Zn,Mg)O.
The coating with a buffer layer takes place, in the related art, in a precipitation reaction, in which various reaction mechanisms, which partially oppose one another, run at the same time. In order to obtain the desired reaction, concentration, temperature and flow speed have to be kept within tight limits.
In the production of buffer layers, the challenge is that, particularly in the CdS precipitation, that undesired colloids created in a secondary reaction do not get to the surface of the substrate to be coated.
It is therefore known in the related art that one should keep the process medium used in motion. For instance, published German patent application document DE 10 2005 025 123 A1 describes that thin-film chalcopyrite-(CIS) solar cells are inserted into an etching solution in a lying position or hanging in a sample holder and exposed for a certain time to the etching solution. In that process, the solution should be able to be stirred manually, by a magnetic stirrer or by ultrasound.
In the related art, it is known alternatively that the substrates are moved over the process medium, so that colloids being created and other undesired particles settle downwards. In this context, it should be noted that, in applying buffer layers, the flow speed of the process medium has to be held within tight limits. Therefore, in order to generate a fluid motion relative to the substrate, according to the related art, the substrate is guided at a certain inclination through the process medium, and a system of rollers situated transversely to the substrate is situated barely above the substrate that is to be coated. The process medium is distributed by the rollers transversely over the substrate and put in motion, and it runs in a planar manner over the substrate until the next roller. There, it is distributed transversely again and mixed together. However, this has the disadvantage that, to be sure, between the rollers an only slightly changed flow speed is able to be provided, but in the area of the rollers, a change in the flow speed does occur. In addition, the rollers have to be situated very tightly over the substrate, so that, in the case of thin substrates, the flow conditions change by the bending of the latter.
It would therefore be desirable to be able to resort to devices which are not afflicted by the disadvantages of the related art, and which would particularly enable the reliable coating of substrates, particularly with buffer layers.